Plasma display panels (PDPs) have been developed as display devices a size of which can be increased easily and which can provide higher definition and higher luminance. A PDP is a device in which phosphors emit light using ultraviolet rays generated through a gas discharge, and thereby images are displayed. In the PDP, a pair of substrates (a front panel and a back panel) are facing each other maintaining predetermined space therebetween, and voltage is applied to the space between the substrates (discharge space) to cause a gas discharge. In order to display a stable image, it is important to maintain airtightness of the discharge space filled with the gas (a discharge gas).
In the PDP, generally, the airtightness of the discharge space is maintained by the following configuration. The peripheries of the front panel and the back panel are sealed together, with a first sealing part. In consideration of the process of producing the PDP, a vent that is used for filling gas in the discharge space is provided in at least one of the front panel and the back panel, and a glass tube used for filling the gas is disposed in an opening portion of the vent. The glass tube and the opening portion are sealed together, with a second sealing part, and further, the glass tube itself is sealed. The peripheries as well as the glass tube and the substrate on which the glass tube has been disposed are sealed together, respectively, by disposing sealing members in predetermined positions and carrying out a predetermined treatment such as heating, for example.
Conventionally, a glass frit made of low-melting glass containing lead oxide has been used often as a sealing member. However, from the viewpoint of environmental protection, there is a need for replacing it with glass that is substantially free from a lead component. The glass compositions that are substantially free from a lead component and that can be used as sealing members are disclosed in JP2001-302279A, JP2001-139344A, JP2000-7375A, JP2002-326838A, and JP2003-238199A, for example. The glass compositions that are disclosed in these publications are used as sealing members in a form of paste in which the compositions are dispersed in a paste vehicle containing resin and/or an organic solvent or in a form of a shaped body (a pressed fit) that is formed using an organic binder.
Each of the glass compositions that are disclosed in the respective publications described above contains P2O5 and SnO as its components. Among them, SnO is susceptible to oxidation or reduction at the time of a sealing process, i.e. the valency of Sn may fluctuate. That is, SnO tends to be changed into SnO2 by the oxidation and also changed into Sn by the reduction. When SnO is oxidized or reduced at the time of sealing, flowability of the glass composition has decreased. Depending on the extent of the flowability decrease, the airtightness of the discharge space formed in the PDP cannot be maintained. As a result, the performance of the PDP may deteriorate in some cases.
Accordingly, there is a demand for PDPs in which the airtightness of the discharge space is maintained and a performance of which does not deteriorate while the PDPs include a sealing part containing P2O5 and SnO. There also is a demand for the sealing members using which such PDPs can be obtained.